Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Environmental Engineering

First Adviser

Brown, Derick G.

Other advisers/committee members

Fox, John T.; Jellison, Kristen L.; Berger, Bryan W.

Abstract

The anaerobic digestion (AD) process uses a series of microbial reactions to convert organic compounds to a methane-rich biogas, and engineered application of this process allows energy recovery from industrial organic waste streams. Poor stability and susceptibility to failure, however, have greatly hindered more frequent application of AD for treatment of industrial wastes. The concern with process stability is particularly true where reactor pH fluctuates due to variations in organic loading. During the organic overloading, the huge difference of growth rate between acetogenic bacteria and methanogenic archaea could induce the accumulation of volatile fatty acids. The accumulated volatile fatty acids will drop pH and the lower pH can cause severe stress conditions on the methanogenic archaea within the reactors. And also heavy metals have been reported to be one of the major causes of digester upset or failure. In present, there are two major ways to alleviate heavy metal toxicity. One is the addition of chemicals, such as sulfide, EDTA and NTA. However, these chemicals are also toxic to anaerobic digester if they are excessive used. The other is the addition of solid surface including activated carbon, kaolin, needle-punctured fabric. These solid materials can be inert or active. Here, this dissertation demonstrated that the iminodiacetate-functionalized ion-exchange fiber (IXF) Fiban X-1 is able to stabilize AD by buffering pH fluctuations and moderating shock-loads of dissolved toxic metals and the anion ion exchange fiber Fiban A-1 was also used to alleviate chromate toxicity successfully. Compared to other active material, it has high regeneration rate, reaction rate, selectivity, capacity and very stable to high alkaline solution. Results provide positive data indicating that IXFs can be used to passively stabilize engineered anaerobic reactors against organic overloading events. Reactors with IXF always have higher pH, methane generation and lower COD concentration than the reactor without IXF during organic overloading events. Also, the relationships among the methane generation, pH and COD with all the data from organic overloading experiments were studied. The result showed that the performance of reactors is proportional to pH. But unexpectedly COD or VFA concentration doesn’t have a clear relationship with normalized methane generation rate. For experiments of the addition of heavy metals, the effluent metal concentration and methane generation proved that the ion exchange capacity helped reactors survived from heavy metals’ toxicity. However, ion exchange capacity exhibited different importance in nickel and copper addition experiment, when they are compared with methane generation of the reactor with glass-fiber that doesn’t have ion exchange capacity. In addition, after exposure, reactors showed a significant pH drop and all of failed reactors had a low pH around 5.

Share

COinS